This invention relates to the fluid catalytic cracking (FCC) of petroleum feedstocks to produce transportation fuels and is especially directed to improvements in FCC to increase the isobutylene and isoamylenes contents of the cracked product.
Increased addition of oxygenated materials to gasoline has been mandated by the US Government. The current industry additives of choice are methyl tertiary butyl ether (MTBE) and tertiary amyl methyl ether (TAME). The technology to make MTBE is well known and commercially viable. Briefly, the ether is manufactured by reacting isobutylene and methanol over a resin catalyst. Obtaining sufficient amounts of isobutylene and isoamylenes at reasonable cost is crucial. In most modern refineries, a dehydroisomerization process can be operated to convert butanes to isobutylene. However, a fluid catalytic cracker is the best if not the only source of making isobutylene and isoamylenes while processing heavy hydrocarbon streams such as gas oil and resid. An FCC catalyst that enhances these olefin yields is essential for viable production of MTBE and TAME in refineries.
It is well known in the literature that lowering the unit cell size (UCS) of a Y zeolite via steaming gives a catalyst which enhances olefin selectivity during the catalytic cracking of hydrocarbons. We have discovered, however, that we can make further improvements in isobutylene and isoamylene yields than by just lowering unit cell size of Y.